As is known, conventional physically narrow antennas, such as balanced sleeve dipole antennas, transmit omni-directional electromagnetic radiation with substantially uniform intensity in all directions. It is often desirable, however, to focus or provide a collimated radiation beam to a particular target, such as in radar target acquisition and/or searching operations. Conventional structures for receiving and converting the omni-directional radiation beam to a collimated radiation beam generally include convergent lenses, angular filters and guided wave horns.
The use of convergent lenses, angular filters or guided wave horns to convert the omni-directional radiation into a collimated beam, however, provides only a mono-directional beam, that is, a collimated beam transmitted in a single direction. In order to provide a bidirectional beam, the convergent lenses, angular filters or guided wave horns would have to be used in pairs, which may contribute to system costs. Furthermore, there can be a significant loss in signal or beam intensity when using convergent lenses or angular filters to convert from the omni-directional radiation beam provided by the antenna to the collimated radiation beam provided by these devices due to inherent losses that occur during the conversion process. Horns may not be particularly lossy, but they are heavy, and thus using them in portable application is undesirable due to their contribution to system weight.
It would, therefore, be desirable to overcome the aforesaid and other disadvantages.